Method of treating bristles



Patented Sept. 22, 1936 UNITED STATES METHOD OF TREATING BRISTLES W Kcdzie Teller, Chicago, Ill., assignor to Weco Products Company; Chicago, 111., a corporation of Illinois No Drawing. Application September 28; 1934, Serial No. 745,941

3 Claims. (or. 91-10) This invention relates to a method of treating bristles for use in the manufacture of brushes, such as tooth brushes, brushes for general toilet purposes, household brushes, paint brushes and the like.

In my copending application Serial No. 707,788, filed January 22, 1934, there is described a method of treating bristles byimpregnating the bristles with a water solution of a partial condensation 10 product of urea and formaldehyde. 1 I have now found that better penetration of the bristles and more satisfactory results can be obtained. if the bristles are treated with an unreacted aqueous mixture of formaldehyde and urea and then com- 35 pleting the condensation reaction after the bristles have first been dried to remove excess water. The present method eliminates the step of partially reacting the resin forming ingredients prior to the impregnation of the bristles. I

m It is therefore an object of this invention to provide a method of treating, bristles to render them less absorptive of water and to impart to the bristles greater body and a longer life of usefulness.

25 It is a further important object ofthis invention to provide a method of impregnating bristles with an aqueous solution of unreacted resin forming ingredients and then subsequently completing the condensation reaction in situ on and within so the bristles.

It is a further important object of this invention to provide a method of impregnating bristles with a urea-formaldehyde type of resin to cause the bristles to retain their rigidity 'for a longer 35 period of time when subjected to the action of water, or aqueous solutions.

Other and further important objects of this invention will become apparent from the following description and appended claims.

- 40 The bristles that may be treated in accordance with my method include all of the various types of bristles known to the art, but the advantages of my method are more apparent in the treatment of inferior grades of bristles, such as those 45 that are hollow or have relatively large pores,

voids or cavities in them, and bristles that are too soft, or limp, or have insumcient body for use in the manufacture of brushes. Also, although not specifically so limited, my invention is of 50 particular applicability in the treatment of bristles for use in tooth brushes. l-leretofore, the better 'grade of tooth brushes have required the use of the highest grade of bristles, usuallyobtained from the solid portions of the bristles of 55 wild boars. The highest grades of bristles are,

however, more expensive and rapidly becoming less available, so that an important feature of my invention is making available bristles of inferior quality as substitutes for the higher quality bristles heretofore used in the manufacture of 5 tooth brushes. In the treatment of bristles according to my method, the bristles are first soaked, or immersed,

in an aqueous solution of urea and formaldehyde.

A suitable solution is prepared from the following 10 formula:

v Parts Urea Formaldehyde (40% aqueous solution) 40 Glacial acetic acid 0.3 15

- it being only necessary to maintain the solution 1 on the acid side, rather than on the alkaline side.

Although an alkaline aqueous solution may be used, more satisfactory results have been obtained by employing an acid aqueous solution of the urea and formaldehyde.

It will, of course, be understood that derivatives' of urea, such as thiourea, may be used in place of urea and that other methylene condensing agents than formaldehyde may be used, such as hexamethylenetetramine. My invention also contemplates the use in the foregoing formula of a small proportion of a phenol, such as phenol itself or cresol, say up to 20% of phenol based on the weight of urea. Where a phenol is used in the formula, the amount of formaldehyde is increased proportionately, using approximately 2 parts of 40% aqueous solution of formaldehyde to each part of phenol added.

The bristles are impregnated w th a solution such as described at ordinary ro 'mtemperatures, so that no reaction takes place between the urea and the formaldehyde either in making up the solution or during impregnation of the bristles with the solution. After the bristles have been thoroughly impregnated, which may require from 5 to 30 minutes, the bristles are removed from 5 the solution and the excess of solution eliminated from the surfaces of the bristles, as by centrifuging. The treated bristles are then dried at a temperature not above 100 F., and preferably at about room temperature, to eliminate excess pre-jelling of the solution, it may be kept cool, say

at 10 C. or less, until it is to be used. The reaction that occurs during the drying step probably results in the formation of a methylol urea. This reaction will not take place, if an organic solvent is used instead of water as the solvent for the urea and formaldehyde.

As a result of this preliminary reaction during the drying operation, there is some tendency of the bristles to stick together, but the adherence of the bristles to each other is only slight and the bristles may be easily disengaged from one another by rolling them upon themselves, using very light pressure. Alternatively, the bundles of bristles, after either partial or complete drying, may be immersed fora short time in alcohol, naphtha, or acetone to soften the outsidecoating and permit separation of the individual bristles. This operation removes some of the surface coating, but that is desirable, as an excess of the condensation product on the surfaces gives rise to dusting when the bristles are used.

After the bristles have been thoroughly dried at temperatures below those at which complete reaction takes place between the resin forming ingredients, the bristles aresubjected to a higher temperature for a short period, suificient to complete the condensation reaction between the urea and formaldehyde. It is preferable to heat the bristles to a temperature between and C. and for a period 'offrom 2 to 3 minutes, since if higher temperatures or longer periods of time are used, there is likelihood of destroying the physical characteristics of the bristles, making them undesirably yellow and brittle. Temperatures below 180 0., however, can be used and the time of treatment increased up to five minutes or so.

Since the bristles are subjected to these temperatures under atmospheric pressures, there is some loss of water due to evaporation and volatilization. This loss of water tends to make the bristlesmore brittle than is desirable, and in order to counteract this tendency, the bristles are preferably subjected to a humidifying step. To this end, the bristles may be subjected to a humid atmosphere for a sumcient period for the bristles to reabsorb their normal amount of water. It has been found satisfactory to leave the bristles overnight in an atmosphere saturated with moisture at room temperatures. One of the advantages of the method just de scribed is that the use of an aqueous solution of unreacted resin forming ingredients gives better penetration of the .bristles, owing to a lower visaoeaeas gredients. It is practically impossible to secure such a high concentration of solids, if any reaction is permitted between the urea andformaldehyde, without so greatly increasing the viscosity as to give poorer impregnation of the bristles.

The finished product prepared in accordance with this invention has a slightly added stifiness over that possessed by the original bristles and this added stiffness is largely retained when the bristles are wet. The urea-formaldehyde condensation product formed in the pores and on the surfaces of the bristles is colorless and sufiiciently flexible to adhere well to the bristles and not crack during use.

Although other catalysts or condensing agents than glacial acetic acid may be used in the preparation of the impregnating solution, best results have been obtained using glacial acetic acid. An

- equivalent degree of acidity may be produced by the use of any mineral acid, such as sulphuric or hydrochloric.

I am aware that numerous details 'of the process may be varied through a wide range without departing from the principles of this invention,

and I, therefore, do not purpose limiting the patent granted hereon otherwise than defined by the appended claims.

I claim as my invention:

1. The method of treating bristles to render them more water resistant without greatly increasing their original stiifness or rigidity, which comprises impregnating said bristles at room temperature, with an aqueous solution of urea, formaldehyde and glacial acetic acid, in the proportion of approximately 20 parts of urea to 40 parts of 40% aqueous solution of formaldehyde to 0.3 part of glacial acetic acid, drying the impregnated bristles to remove water therefrom, and heating said impregnated bristles to a temperature of between 1'75 and 180 C. for a period of from 2 to 3 minutes to effect condensation of urea and formaldehyde.

2. The method of treating bristles to render them .more water resistant without greatly increasing their original stifiness or rigidity, which comprising impregnating bristles in a low viscosity aqueous solution of unreacted resin forming ingredients of the urea-formaldehyde type, drying the impregnated bristles, heating said dried-bristles to effect the condensation of said ingredients to form a resin within and on said bristles and conditioning said bristles to restore a normal moisture content thereto.

3. The method of treating bristles to render them more water resistant'without greatly increasing the original stifiness or rigidity of the bristles, which comprises impregnating said bristles in the cold with a low viscosity aqueous solution of an unreacted mixture of a urea and a methylene condensing agent, the latter being in excess of reacting proportions, and a small percentage of an acid, removing excess moisture from the bristles and heating said bristles to a temperature not'above aboutl80 C. for a sufficien't time to complete the condensation reaction between the urea and condensing agent without destroying the physical characteristics of the bristles. 1

W KEDZIE TELLER. 

